This invention relates to ultrasonic imaging and more particularly to suppression of spurious artifact signals at ranges close to an excitation source, herein known as ring-down artifact.
Ring-down artifact is caused by transients associated with an exciter which cause interference with informational signals reflected from sources close to the exciter (echo signals). In close-in imaging, such as in intravascular structures, undesired ring-down artifact can impede accurate imaging.
One known mechanism for eliminating ring-down artifact is to gate on the echo signal so that all artifacts are eliminated in the close-in region where ring-down is expected to occur. However, useful echo signals are also eliminated by gating.
Another method described in U.S. Pat. No. 5,601,082, the disclosure of which is herein incorporated by reference, is to generate a reference scan to develop a long-term average and use the reference scan to subtract on all but useful echo signals. However, subtraction of a reference scan may also remove useful echoes having a time constant of the same order of magnitude as the averaged reference scan. Thus subtraction based on a simple reference scan is inadequate to analyze a full range of signal types. What is needed is a more accurate technique for identifying ring-down artifact so it can be separated from legitimate signals.